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| Abstract
A method and apparatus for simulation of hearing in mammals by introduction
of a plurality of microwaves into the region of the auditory cortex
is shown and described. A microphone is used to transform sound signals
into electrical signals which are in turn analyzed and processed to
provide controls for generating a plurality of microwave signals at
different frequencies. The multifrequency microwaves are then applied
to the brain in the region of the auditory cortex. By this method sounds
are perceived by the mammal which are representative of the original
sound received by the microphone.
---------- Inventors: Stocklin; Philip L. (P.O. Box 2111, Satellite Beach, FL
32937) Current U.S. Class: 607/45; 607/56 ---------- References Cited [Referenced By]
---------- Foreign Patent Documents Other References
Gerkin, G., "Electroencephalography & Clinical Neurophysiology", vol.
135, No. 6, Dec. 1973, pp. 652-653. Primary Examiner: Kamm; William E. ---------- What is claimed is:
1. A sound perception device for providing induced perception of sound
into a mammalian brain comprising in combination:
means for generating microwave radiation which is representative of
a sound to be perceived, said means for generating including means for
generating a simultaneous plurality of microwave radiation frequencies
and means for adjusting the amplitude of said microwave radiation frequencies
in accordance with the sound to be perceived; and
antenna means located in the region of the auditory cortex of said
mammalian brain for transmitting said microwave energy into the auditory
cortex region of said brain.
2. A hearing device for perception of sounds comprising in combination:
means for generating a signal representative of sounds;
means for analyzing said signal representative of said sounds having
an output;
means for generating a plurality of microwave signals having different
frequencies having a input connected to said output of said means for
analyzing said signals, having an output;
means for applying said plurality of microwave signals to the head
of a subject, and
whereby the subject perceives sounds which are representative of said
sounds.
3. The apparatus in accordance with claim 2 wherein said means for
generating a signal is a microphone for detecting sound waves.
4. The apparatus in accordance with claim 2 wherein said means for
applying said plurality of microwave signals is an antenna.
5. The apparatus in accordance with claim 4 wherein said antenna is
placed in the region of the auditory cortex of the subject.
6. The apparatus in accordance with claim 2 wherein the subject is
a human being.
7. The apparatus in accordance with claim 2 wherein said means for
analyzing said signal comprises: an acoustic filter bank for dividing
said sounds into a plurality of component frequencies; and a mode control
matrix means for providing control signals which are weighted in accordance
with said plurality of component frequencies, having an output connected
to said means for generating a plurality of microwave signal inputs.
8. The apparatus in accordance with claim 7 wherein said acoustic
filter bank includes a plurality of audio frequency filters.
9. The apparatus in accordance with claim 8 wherein said audio frequency
filters provide a plurality of output frequencies having amplitudes
which are a function of said signal representative of sounds.
10. The apparatus in accordance with claim 9 wherein said amplitudes
are the weighted in accordance with transform function of the signal
representative of sounds.
11. The apparatus in accordance with claim 7 wherein said mode control
matrix device includes a voltage divider connected to each of said plurality
of said audio frequency filters.
12. The apparatus in accordance with claim 11 wherein each of said
voltage dividers has a plurality of outputs which are connected in circuit
to said means for generating a plurality of microwave signals.
13. The apparatus in accordance with claim 2 wherein said means for
generating a plurality of microwave signals comprises a plurality of
microwave generators each having a different frequency and means for
controlling the output amplitude of each of said generators.
14. The apparatus in accordance with claims 2 wherein said means for
generating a plurality of microwave signals comprises a broad band microwave
source and a plurality of filters.
15. The apparatus in accordance with claim 13 wherein said generators
each comprise a microwave signal source and a gain controlled microwave
amplifier.
16. The apparatus in accordance with claim 13 wherein said means for
analyzing output is connected to said means for controlling microwave
amplifier output amplitudes.
17. The apparatus in accordance with claim 13 wherein analyzing includes
K audio frequency filters.
18. The apparatus in accordance with claim 17 wherein there are N
microwave generators.
19. The apparatus in accordance with claim 18 including a mode partitioning
means which provides N outputs for each of said K audio frequency filters.
20. The apparatus in accordance with claim 19 wherein said N amplifiers
each have K inputs from said mode partitioning means.
21. The apparatus in accordance with claim 20 wherein said N amplifiers
have K inputs less the mode partitioning means outputs which are so
small that they may be omitted.
22. The apparatus in accordance with claim 20 wherein said mode partitioning
output device outputs each include a diode connected to each microwave
amplifier gain control to provide isolation between all outputs.
23. The apparatus in accordance with claim 20 wherein said K audio
frequency filters are chosen to correspond to the critical bandwidths
of the human ear.
24. The apparatus in accordance with claim 20 wherein said N microwave
generators are each adjustable in frequency output.
25. The apparatus in accordance with claim 18 wherein the frequency
of each N microwave generators is determined by anatomical estimation.
26. The apparatus in accordance with claim 18 wherein the frequency
of the lowest frequency microwave generator is chosen by determination
of the effect of external microwave generation on the EEG of the subject.
27. The apparatus in accordance with claim 18 wherein the frequency
of each of said N microwave generators corresponds to the subject's
microwave modal frequencies.
28. The apparatus in accordance with claim 27 wherein the subject's
modal frequencies are determined by measurement of the subject's cephalic
index and the lateral dimensions of the skull.
29. The apparatus in accordance with claim 28 wherein the subject's
lowest modal frequency is determined by varying the frequency of the
lowest frequency microwave generator about the estimated value until
a maximum acoustic perception is obtained by the subject.
---------- Description ----------
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to devices for aiding of hearing in mammals.
The invention is based upon the perception of sounds which is experienced
in the brain when the brain is subjected to certain microwave radiation
signals.
2. Description of the Prior Art
In prior art hearing devices for human beings, it is well known to
amplify sounds to be heard and to apply the amplified sound signal to
the ear of the person wearing the hearing aid. Hearing devices of this
type are however limited to hearing disfunctions where there is no damage
to the auditory nerve or to the auditory cortex. In the prior art, if
there is damage to the auditory cortex or the auditory nerve, it cannot
be corrected by the use of a hearing aid.
During World War II, individuals in the radiation path of certain
radar installations observed clicks and buzzing sounds in response to
the microwave radiation. It was through this early observation that
it became known to the art that microwaves could cause a direct perception
of sound within a human brain. These buzzing or clicking sounds however
were not meaningful, and were not perception of sounds which could otherwise
be heard by the receiver. This type of microwave radiation was not representative
of any intelligible sound to be perceived. In such radar installations,
there was never a sound which was generated which resulted in subsequent
generation of microwave signals representative of that sound.
Since the early perception of buzzing and clicking, further research
has been conducted into the microwave reaction of the brain. In an article
entitled "Possible Microwave Mechanisms of the Mammalian Nervous System"
by Philip L. Stocklin and Brain F. Stocklin, published in the TIT Journal
of Life Sciences, Tower International Technomedical Institute, Inc.
P.O. Box 4594, Philadelphia, Pa. (1979) there is disclosed a hypothesis
that the mammalian brain generates and uses electro magnetic waves in
the lower microwave frequency region as an integral part of the functioning
of the central and peripheral nervous systems. This analysis is based
primarily upon the potential energy of a protein integral in the neural
membrane.
In an article by W. Bise entitled "Low Power Radio-Frequency and Microwave
Effects On Human Electroencephalogram and Behavior", Physiol. Chemistry
Phys. 10, 387 (1978), it is reported that there are significant effects
upon the alert human EEG during radiation by low intensity CW microwave
electromagnetic energy. Bise observed significant repeatable EEG effects
for a subject during radiation at specific microwave frequencies.
SUMMARY OF THE INVENTION
Results of theoretical analysis of the physics of brain tissue and
the brain/skull cavity, combined with experimentally-determined electromagnetic
properties of mammalian brain tissue, indicate the physical necessity
for the existence of electromagnetic standing waves, called modes in
the living mammalian brain. The mode characteristics may be determined
by two geometric properties of the brain; these are the cephalic index
of the brain (its shape in prolate spheroidal coordinates) and the semifocal
distance of the brain (a measure of its size). It was concluded that
estimation of brain cephalic index and semifocal distance using external
skull measurements on subjects permits estimation of the subject's characteristic
mode frequencies, which in turn will permit a mode by mode treatment
of the data to simulate hearing.
This invention provides for sound perception by individuals who have
impaired hearing resulting from ear damage, auditory nerve damage, and
damage to the auditory cortex. This invention provides for simulation
of microwave radiation which is normally produced by the auditory cortex.
The simulated brain waves are introduced into the region of the auditory
cortex and provide for perceived sounds on the part of the subject.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the acoustic filter bank and mode control matrix portions
of the hearing device of this invention.
FIG. 2 shows the microwave generation and antenna portion of the hearing
device of this invention.
FIG. 3 shows a typical voltage divider network which may be used to
provide mode partition.
FIG. 4 shows another voltage divider device which may be used to provide
mode partition.
FIG. 5 shows a voltage divider to be used as a mode partition wherein
each of the resistors is variable in order to provide adjustment of
the voltage outputs.
FIG. 6 shows a modified hearing device which includes adjustable mode
partitioning, and which is used to provide initial calibration of the
hearing device.
FIG. 7 shows a group of variable oscillators and variable gain controls
which are used to determine hearing characteristics of a particular
subject.
FIG. 8 shows a top view of a human skull showing the lateral dimension.
FIG. 9 shows the relationship of the prolate spherical coordinate
system to the cartesian system.
FIG. 10 shows a side view of a skull showing the medial plane of the
head, section A--A.
FIG. 11 shows a plot of the transverse electric field amplitude versus
primary mode number M.
FIG. 12 shows a left side view of the brain and auditory cortex.
FIG. 13 shows the total modal field versus angle for source location.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention is based upon observations of the physical mechanism
the mammalian brain uses to perceive acoustic vibrations. This observation
is based in part upon neuro anatomical and other experimental evidence
which relates to microwave brain stimulation and the perception of sounds.
It is has been observed that monochromatic acoustic stimuli (acoustic
tones, or single tones) of different frequencies uniquely stimulate
different regions of the cochlea. It has also been observed that there
is a corresponding one to one relationship between the frequency of
a monochromatic acoustic stimulus and the region of the auditory cortex
neurally stimulated by the cochlear nerve under the physiologically
normal conditions (tonotopicity).
It is has been observed that for an acoustic tone of a frequency which
is at the lower end of the entire acoustical range perceivable by a
person, that a thin lateral region ("Line") parallel to the medial axis
of the brain and toward the inferior portion of the primary auditory
cortex is stimulated. For an acoustic tone whose frequency is toward
the high end of the entire perceivable acoustic range, a thin lateral
region parallel to the medial axis and toward the superior portion of
the primary auditory cortex is stimulated.
Neural stimulation results in the generation of a broad band of microwave
photons by the change in rotational energy state of protons integral
to the neuron membrane of the auditory cortex. The physical size and
shape of the brain/skull cavity, together with the (semi-conductor)
properties (conductivity and dielectric constant) of the brain tissue
provide an electromagnetic resonant cavity. Specific single frequencies
are constructively reinforced so that a number of standing electromagnetic
waves, each at its own single electromagnetic frequency in the microwave
frequency region, are generated in the brain. Each such standing electromagnetic
wave is called a characteristic mode of the brain/skull cavity.
Analysis in terms of prolate spheroidal wave functions indicates that
transverse electric field components of these modes have maxima in the
region of the auditory cortex. This analysis further shows that transverse
electric field possess a variation of amplitude with angle in the angular
plane (along the vertical dimension of the auditory cortex) and that
is dependent only upon the primary mode number.
The auditory cortex in the normally functioning mammalian brain is
a source of microwave modes. The auditory cortex generates these modes
in accordance with the neural stimulation of the auditory cortex by
the cochlear nerve. Mode weighting for any one acoustic tone stimulus
is given by the amplitude of each mode along the line region of the
auditory cortex which is neurally stimulated by that acoustic tone stimulus.
A listing of mode weighting versus frequency of acoustic stimulus is
called the mode matrix.
In this invention, the functions of the ear, the cochlear nerve, and
the auditory cortex are simulated. Microwaves simulating the mode matrix
are inserted directly into the region of the auditory cortex. By this
insertion of simulated microwave modes, the normal operation of the
entire natural hearing mechanism is simulated.
Referring now to FIG. 1 and FIG. 2 there is shown an apparatus which
provides for induced perception of sound into a mammalian brain. This
hearing device includes a microphone 10 which receives sounds, an acoustic
filter bank 12 which separates the signals from the microphone into
component frequencies, and a mode control matrix 14 which generates
the mode signals which are used to control the intensity of microwave
radiations which are injected into the skull cavity in the region of
the auditory. cortex.
The acoustic filter bank 12 consists of a bank of acoustic filters
F1 through Fk which span the audible acoustic spectrum. These filters
may be built from standard resistance, inductance, and capacitance components
in accordance with well established practice. In the preferred embodiment
there are 24 filters which correspond to the observed critical bandwidths
of the human ear. In this preferred embodiment a typical list of filter
parameters is given by Table 1 below:
Connected to each microwave amplifier gain control line is a mode
simulation device 16 which receives weighted mode signals from the mode
partition devices 14. Each mode simulation device consists of one through
k lines and diodes 17 which are each connected to summing junction 19.
The diodes 17 provide for isolation from one mode partition device to
the next. The diodes 17 prevent signals from one mode partition device
from returning to the other mode partition devices which are also connected
to the same summing junction of the mode summation device 16. The diodes
also serve a second function which is the rectification of the signals
received from the acoustic filter bank by way of the mode partition
devices. In this way each mode partition device output is rectified
to produce a varying DC voltage with major frequency components of the
order of 15 milliseconds or less. The voltage at the summation junction
19 is thus a slowly varying DC voltage.
The example mode partition devices are shown in greater detail in
FIGS. 3, 4, and 5. The mode partition devices are merely resistance
networks which produce 1 through N output voltages which are predetermined
divisions of the input signal from the acoustic filter associated with
the mode partition device. FIG. 3 shows a mode partitioning device wherein
several outputs are associated with each series resistor 30. In the
embodiment depicted in FIG. 4 there is an output associated with each
series resistor only, and thus there are N series resistors, or the
same number of series resistors as there are outputs. The values of
the resistors in the mode partition resistor network are determined
in accordance with the magnitudes of the frequency component from the
acoustic filter bank 12 which is required at the summation point 19
or the gain control line for amplifiers 20.
The microwave amplifier bank 18 consists of a plurality of microwave
oscillators 1 through N each of which is connected to an amplifier 20.
Since the amplifiers 20 are gain controlled by the signals at summation
junction 19, the magnitude of the microwave output is controlled by
the mode control matrix outputs F1 through F.sub.n. In the preferred
embodiment there are 24 amplifiers.
The leads from the microwave oscillators 1 through N to the amplifiers
20 are shielded to prevent cross talk from one oscillator to the next,
and to prevent stray signals from reaching the user of the hearing device.
The output impedance of amplifiers 20 should be 1000 ohms and this is
indicated by resistor 21. The outputs of amplifiers 20 are all connected
to a summing junction 22. The summing junction 22 is connected to a
summing impedance 23 which is approximately 50 ohms. The relatively
high amplifier output impedance 21 as compared to the relatively low
summing impedance 23 provides minimization of cross talk between the
amplifiers. Since the amplitude of the microwave signal needed at the
antenna 24 is relatively small, there is no need to match the antenna
and summing junction impedances to the amplifier 20 output impedances.
Efficiency of the amplifiers 20 is not critical.
Level control of the signal at antenna 24 is controlled by pick off
25 which is connected to the summing impedance 23. In this manner, the
signal at antenna 24 can be varied from 0 (ground) to a value which
is acceptable to the individual.
The antenna 24 is placed next to the subject's head and in the region
of the subject's auditory cortex 26. By placement of the antenna 24
in the region of the auditory cortex 26, the microwave field which is
generated simulates the microwave field which would be generated if
the acoustic sounds were perceived with normal hearing and the auditory
cortex was functioning normally.
In FIG. 2A there is shown a second embodiment of the microwave radiation
and generator portion of the hearing device. In this embodiment a broad
band microwave source 50 generates microwave signals which are feed
to filters 52 through 58 which select from the broad band radiation
particular frequencies to be transmitted to the person. As in FIG. 2,
the amplifiers 20 receive signals on lines 19 from the mode control
matrix. The signals on lines 19 provide the gain control for amplifiers
20.
In FIG. 6 there is shown a modified microwave hearing generator 60
which includes a mode partition resistor divider network as depicted
in FIG. 5. Each of the mode partition voltage divider networks in this
embodiment are individually adjustable for all of the resistances in
the resistance network. FIG. 5 depicts a voltage division system wherein
adjustment of the voltage partition resistors is provided for.
In FIG. 6, the sound source 62 generates audible sounds which are
received by the microphone of the microwave hearing generator 60. In
accordance with the operation described with respect to FIGS. 1 and
2, microwave signals are generated at the antenna 10 in accordance with
the redistribution provided by the mode control matrix as set forth
in FIG. 5.
The sound source 62 also produces a signal on line 64 which is received
by a head phone 66. The apparatus depicted in FIG. 6 is used to calibrate
or fit a microwave hearing generator to a particular individual. Once
the hearing generator is adjusted to the particular individual by adjustment
of the variable resistors in the adjustable mode partition portion of
the hearing generator, a second generator may be built using fixed value
resistors in accordance with the adjusted values achieved in fitting
the device to the particular subject. The sound produced by headphone
66 should be the same as a sound from the sound source 62 which is received
by the microphone 10 in the microwave hearing generator 60. In this
way, the subject can make comparisons between the perceived sound from
the hearing generator 60, and the sound which is heard from headphone
66. Sound source 62 also produces a signal on 68 which is feed to cue
light 69. Cue light 69 comes on whenever a sound is emitted from sound
source 62 to the microwave generator 60. In this manner, if the subject
hears nothing, he will still be informed that a sound has been omitted
and hence that he is indeed perceiving no sound from the microwave hearing
generator 60.
In FIG. 7 there is shown a modified microwave hearing generator which
may be used to determine a subject's microwave mode frequencies. In
this device, the acoustic filter bank and the mode control matrix have
been removed and replaced by voltage level signal generated by potentiometers
70. Also included are a plurality of variable frequency oscillators
72 which feed microwave amplifiers 74 which are gain controlled from
the signal generated by potentiometers 70 and pick off arm 76.
This modified microwave hearing generator is used to provide signals
using one oscillator at a time. When an oscillator is turned on, the
frequency is varied about the estimated value until a maximum acoustic
perception by the subject is perceived. This perception however may
consist of a buzzing or hissing sound rather than a tone because only
one microwave frequency is being received. The first test of perception
is to determine the subject's lowest modal frequency for audition (M=1).
Once this modal frequency is obtained, the process is repeated for several
higher modal frequencies and continued until no maximum acoustic perception
occurs.
Another method of determination of a subject's modal frequencies is
through anatomical estimation. This procedure is by measurement of the
subject's cephalic index and the lateral dimensions of the skull. In
this method, the shape is determined in prolate spheroidal coordinance.
Purely anatomical estimation of subject's modal frequencies is performed
by first measuring the maximum lateral dimension (breadth) L FIG. 8,
of the subject's head together with the maximum dimension D (anterior
to posterior) in the medial plane of the subject's head. D is the distance
along Z axis as shown in FIG. 10. The ratio L/D, called in anthropology
the cephalic index, is monotonically related to the boundary value .xi..sub.o
defining the ellipsoidal surface approximating the interface between
the brain and the skull in the prolate spheroidal coordinate system.
.xi..sub.o defines the shape of this interface; .xi..sub.o and D together
give an estimate of a, the semi-focal distance of the defining ellipsoid.
Using .xi..sub.o and a, together with known values of the conductivity
and dielectric constants of brain tissue, those wavelengths are found
for which the radial component of the electric field satisfies the boundary
condition that it is zero at .xi..sub.o. These wavelengths are the wavelengths
associated with the standing waves or modes; the corresponding frequencies
are found by dividing the phase velocity of microwaves in brain tissue
by each of the wavelengths.
A subject's microwave modal frequencies may also be determined by
observing the effect of external microwave radiation upon the EEG. The
frequency of the M equal 1 mode may then be used as a base point to
estimate all other modal frequencies.
A typical example of such an estimation is where the subject is laterally
irradiated with a monochromatic microwave field simultaneous with EEG
measurement and the microwave frequency altered until a significant
change occurs in the EEG, the lowest such frequency causing a significant
EEG change is found. This is identified as the frequency of the M=1
mode, the lowest mode of importance in auditory perception. The purely
anatomical estimation procedure (FIGS. 8, 9, 10) is then performed and
the ratio of each modal frequency to the M=1 modal frequency obtained.
These ratios together with the experimentally-determined M=1 frequency
are then used to estimate the frequencies of the mode numbers higher
than 1. The prolate spheroidal coordinate system is shown in FIG. 9.
Along the lateral plane containing the x and y coordinates of FIG. 9,
the prolate spheroidal coordinate variable .phi. (angle) lies FIGS.
9 and 10. Plots of the transverse electric field amplitude versus primary
mode number m are shown in FIG. 11. The equation is
E.sub.transverse (m, .phi.)=E.sub.o sin(m .phi.)
The "elevation view" FIG. 12, of the brain from the left side, shows
the primary auditory cortex 10. The iso-tone lines and the high frequency
region are toward the top of 100 and the low frequency region toward
the bottom of 100.
The formula I, set forth below is the formula for combining modes
from an iso-tone line at .phi.=.phi.j being excited to obtain the total
modal field at some other angular location .phi.. For this formula,
if we let J=1 (just one iso-tone single frequency acoustic stimulus
line), then it can be shown that ALL modes (in general) must be used
for any ONE tone. ##EQU1## .phi.=ANGLE (0.degree. LATERAL) .phi..sub.j
=LOCATION OF j-TH SOURCE (TOTAL NUMBER J)
.DELTA..phi..sub.m =ATTENUATION LENGTH (IN ANGLE) OF m-TH MODE
m=PRIMARY MODE NUMBER (HIGHEST MODE M)
FIG. 13 shows the resulting total modal field versus angle .phi. for
source location .phi. at 5.25.degree., 12.5.degree., etc. With reference
to the set of curves at the left top of this figure. A spacing of approximately
7.25.degree. in .phi. corresponds to a tonal difference of about 1 octave.
This conclusion is based on the side-lobes of pattern coming from .phi.=5.25.degree.,
etc. The total filed (value on y-axis) falls considerably below the
top curves for source locations well below 5.25.degree. (toward the
high acoustic stimulus end) and also as the source of frequency goes
well above 30.degree. (low frequency end). .phi. is plotted positive
downward from 0.degree. at lateral location as indicates in FIG. 11.
Resistor weightings are obtained from the .vertline.sin (m[.phi.-.phi.j]).vertline.,
Formula I. The scale between acoustic frequency and .phi. must be set
or estimated from experiment. Approximately 5.25.+-.1.degree. corresponds
to a tonal stimulus at about 2 kHz (the most sensitive region of the
ear) since this source location gives the highest electric field amplitude.
The apparatus of FIG. 7 may also be used to determine values for a
hearing device which are required for a particular subject. Once the
modal frequencies have been estimated, the device of FIG. 7 which includes
variable microwave oscillators may be used to determine values for the
oscillators which match the subject, and to determine resistance values
associated with the mode partition devices of the mode control matrix.
In FIG. 7 manual control of the amplifier gain is achieved by potentiometers
76. In this manner the amplifier gains are varied about the estimated
settings for an acoustic tone stimulus in the region of two thousand
Hertz (2 kHz) until maximum acoustic perception and a purest tone are
achieved together. The term purest tone may also be described as the
most pleasing acoustic perception by the subject. This process may be
repeated at selected frequencies above and below 2 kHz. The selected
frequencies correspond to regions of other acoustic filter center frequencies
of the subject. When modal frequency (oscillator frequency) and gain
set values (setting a potentiometer 76) are noted, it is then possible
to calculate fixed oscillator frequencies and control resistor values
for the adjusted hearing device for this particular subject.
In the event the subject has no prior acoustic experience, that is
deaf from birth, estimated resistor values must be used. Also, a complex
acoustic stimulation test including language articulation and pairs
of harmonically related tones may be developed to maximize the match
of the hearing device parameters for those of this particular subject.
Typical components for use in this invention include commercially
available high fidelity microphones which have a range of 50 Hz to 15
kHz with plus or minus 3 dB variation.
The audio filters to be used with the acoustic filter bank 12 are
constructed in a conventional manner, and have Q values of about 6.
The filters may also be designed with 3 dB down points (1/2 the bandwidth
away from the center frequency) occurring at adjacent center frequency
locations.
The diodes 17 in the mode control matrix which provide isolation between
the mode partition circuits are commercially available diodes in the
audio range.
The microwave oscillators 1 through N and the microwave amplifiers
20 are constructed with available microwave transistors which can be
configured either as oscillators or amplifiers. Examples of the transistors
are GaAsFET field effect transistors by Hewlitt Packard known as the
HFET series or silicone bipolar transistors by Hewlitt Packard known
as the HXTR series.
All the cable between the oscillators, the microwave amplifiers, and
the antenna should be constructed with either single or double shielded
coaxial cable.
The antenna 24 for directing microwave signals to the audio cortex
26 should be approximately the size of the auditory cortex. A typical
size would be one and one half CM high and one half to one CM wide.
The antenna as shown is located over the left auditory cortex, but the
right may also be used. Since the characteristic impedance of the brain
tissue at these microwave frequencies is close to 50 ohms, efficient
transmission by commercially available standard 50 ohm coax is possible.
The invention has been described in reference to the preferred embodiments.
It is, however, to be understood that other advantages, features, and
embodiments may be within the scope of this invention as defined in
the appended claims.
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